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101 Cards in this Set
- Front
- Back
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What has nature provided to protect the brain from being deprived of blood?
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Extensive anastomoses in the cerebrovascular system.
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What are 2 types of cerebrovascular anastomoses?
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-Intracranial
-Extracranial |
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What are the 2 intracranial anastomoses?
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-Circle of Willis
-Cortical between ACA, MCA, and PCA on the hemisphere surfaces |
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What is the most important anastomosis?
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Circle of willis
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What are the 2 extracranial anastomoses?
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-Connections between ICA and ECA via Ophthalmic/meningial aa.
-The two ECA's connect, and each connects with vertebral aa too |
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What type of cerebral artery occlusion will result in neurological manifestation? Why?
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Rapid onset - because there is no time for collateral circulation to adapt, so an infarct develops.
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When there is a complete cerebrovascular occlusion, what part of the territory perfused will be affected most/least?
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Most: proximal portion of territory
Least affected: distal portion |
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Why will the proximal portion of a territory be affected the worst by a total occlusion?
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Because the distal portion receives collateral circulation
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When there is an incomplete cerebrovascular occlusion, what part of the territory perfused will be affected most/least?
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Most: the distal portion
Least: the proximal portion |
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Why will the distal portion be affected the worst by an incomplete occlusion? (2 reasons)
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-The flow change is not enough to open collateral circulation
-The last field of irrigation receives the least supply |
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What % of the total body weight is the brain? How much of the body's inspired O2 does it consume?
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2% of body weight
20% of oxygen consumption! |
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What does the brain use all that oxygen for?
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Glucose metabolism
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How long can the brain survive total oxygen deprivation?
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Only a few minutes
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What is more of a factor in cerebral circulation; BP or CO?
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Cardiac output
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Why wouldn't severe hypotension affect cerebrocirculation much?
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Because the cerebrovascular resistance can be increased rather easily to maintain bloodflow.
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How does the cerebrovasculature respond to High PO2 or low PCO2?
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Moderate vasoconstriction
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How does the cerebrovasculature respond to Low PO2 or High PCO2?
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Marked vasodilation
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What are the 3 major cerebrovascular diseases?
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1. Infarction
2. Hemorrhage 3. Hypoxic encephalopathy |
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What is Infarction responsible for in the brain?
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80% of strokes
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What is the cause of brain infarction?
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Occlusion or compression of a cerebral vessel, depriving blood supply to a localized area.
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What is the result of lack of bloodsupply?
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No fresh nutrients
Old waste products build up |
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What are the early consequences of toxic metabolic waste products accumulating in the brain?
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1. Necrosis - death of neurons
2. Reaction of glial cells 3. Vascular proliferation |
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What are the later consequences of toxic metabolic waste products accumulating in the brain?
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1. Liquefaction
2. Gliosis 3. Cavitation |
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What are 3 etiological causes of brain infarction? Which is the most predominant cause of stroke?
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1. Thrombosis - 70% of strokes
2. Embolism 3. Mechanical compression of a vessel |
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If cerebral infarction causes 80% of strokes, what are the other 20% due to?
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Hemorrhage
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What % of strokes (including those caused by both infarcts and hemorrhage) are due to thrombosis?
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70%
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Then what % of strokes are due to embolism or mechanical compression of a vessel?
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10%
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What is thrombosis of a cerebral vessel usually caused by?
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-Atherosclerosis of major aa
-Arteriolosclerosis of arterioles |
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Which cerebral vessels are more often involved in thrombosis leading to brain infarction?
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Extracranial
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What is the most common site of an extracranial thromosis due to arteriosclerotic occlusion?
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At the bifurcation of hte internal and external carotid arteries.
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At what 3 other sites do thromboses occur (in decreasing order of frequency)?
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ACA - 19%
MCA - 13% Vertebrobasilar occlusion 12% |
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What % of thromboses are seen in the Internal carotid?
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56% (most common site)
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What are 3 causes of arteritis leading to thrombosis/infarction other than atherosclerosis and arteriolosclerosis?
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-Collagen diseases
-Infections -Genetics |
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What vessel type will be more often affected by these other causes, and what distribution will be seen?
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-Arterioles
-More disseminated |
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In what 2 conditions will arteriolosclerosis of the brain more usually be seen?
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-Hypertension
-Diabetes |
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What type of infarcts are often seen in these cases? Where?
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Multiple, Small, Lacunar infarcts in the basal ganglia and pons
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What % of strokes are due to Embolism?
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10%
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What are the 3 most common origins of cerebral embolism?
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-Cardiac
-Mural thrombi -Atheromatous plaques |
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What are the 3 typical causes of cardiac embolism?
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-Myocardial infarction
-Endocarditis -Mitral stenosis |
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What complication is often seen in cerebral embolism?
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Hemorrhage - due to lysis of the embolism, resulting in increased shear force of bloodflow which can rupture the blood vessel.
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Why does Mechanical compression lead to brain infarction?
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Because whenever there is increased intracranial pressure it will cause herniation of brain tissue from one compartment into another.
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What is herniation of the uncus into the posterior fossa through the edge of the tentorium called?
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Uncal or Transtentorial herniation
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What is herniation of the cerebellar tonsils into foramen magnum called?
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Tonsillar herniation
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What is it called when the cingulate gyrus from one hemisphere herniates into the other hemisphere?
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Subfalcine herniation
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How does herniation cause infarction?
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The vessels get compressed as brain matter gets pressed against the sharp edge of dura mater.
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What 2 vessels and nerve will get compressed by Uncal herniation?
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-PCA
-ACA -Oculomotor nerves |
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What artery will get compressed by Subfalcine herniation?
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ACA
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What will get compressed by Tonsillar herniation?
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The medulla
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What can result from such medullary compression?
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-Cardiorespiratory arrest
-Death |
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What is suprisingly rare with tonsillar herniation?
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Compression of PICA
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What happens to cerebral bloodflow in general as ICP increases?
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Cerebral bloodflow decreases
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When will cerebral bloodflow be completely ceased?
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When ICP = MAP
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How does the onset of clinical signs and symptoms differ when infarction is caused by thrombosis versus embolism?
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Thrombosis = gradual onset
Embolism = sudden |
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What is the usual patient outcome in brain infarctions?
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The patients usually recover though often with neurological deficits.
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What direct effect can hypertension have on the brain?
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Acute Hypertensive Encephalopathy
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What 3 components make up Acute Hypertensive Encephalopathy?
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-Increased bp in the brain
-Congestion/edema of the brain -Increased ICP |
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What causes 20% of brain strokes?
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Hemorrhage
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What type of signs/symptoms will a brain hematoma produce?
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Those of a space-occupying lesion
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Why do hemorrhages cause strokes, if no blood vessel occlusion is occurring?
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Because the surrounding tissue is destroyed, resulting in necrosis and edema of brain tissue.
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What are 4 causes of brain hemorrhage?
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-Arterial hypertension
-Aneurysm -A-V malformations, angiomas, telangiectasias -Blood dyscrasias |
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What is the most common cause of brain hemorrhage?
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Arterial hypertension
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What is by far the most common site of intracranial hemorrhage due to arterial hypertension?
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Basal ganglia and Putamen
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What are the 3 next most common sites of intracranial hemorrhage?
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-White magger near trigone of lateral ventricle
-Cerebellum -Pons |
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Why does arterial hypertension cause brain hemorrhage?
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Because high pressure bloodflow from large vessels can rupture the thin walls of smaller take-off vessels.
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What are 2 other mechanisms of hemorrhage in arterial hypertension?
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-Micro-aneurysm rupture
-Prehemorrhagic infarct weakens blood vessel, results in a bleed |
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What are the 2 classes of aneurysms?
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-Congenital
-Secondary |
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Where do congenital aneurysms most commonly occur?
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At bifurcations of arteries
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What are 3 causes of secondary aneurysms?
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-Trauma
-Infections -Atherosclerosis |
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What type of aneurysm is seen when caused by atherosclerosis?
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Fusiform
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Are fusiform aneurysms likely to rupture?
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no
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What are 4 possible complications of aneurysms?
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1. Rupture/bleed into subarachnoid and intracerebral space
2. Form thrombi and embolize 3. Compression and irritation of adjacent tissue 4. Arterial spasm |
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What are Telangiectasias?
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A Vascular malformations
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What are Telangiectasias composed of?
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Congories of dilated capillaries separated by neural parenchyma
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Where are telangiectasias often situated?
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-Brainstem
-Basal ganglia |
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What does an AV malformation contain?
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-Abnormal arteries and/or
-Capillaries and/or -Veins Some may be separated by neural tissue |
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What is an Angioma composed of?
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EITHER arteries, capillaries, or veins; NOT separated by neural tissue
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What is the most common angioma?
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Cavernous hemangioma
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What are 2 blood dyscrasias that can cause secondary hemorrhage?
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Leukemia and Hemophilia
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What arteritis condition can cause hemorrhage?
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Lupus SLE
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What is the typical number and distribution of hemorrhages caused by blood dyscrasias or arteritis?
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-Multiple hemorrhages
-Random distribution in brain |
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What is the usual outcome of brain hemorrhages?
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More grave than for infarcts
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Why is cerebral hemorrhage generally worse than infarction?
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Because the extravasation of blood results in increased ICP
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What 4 clinical manifestations are commonly seen in cerebral hemorrhaging?
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1. Focal neurological deficits
2. Severe headache 3. Coma 4. Death |
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What 2 complications often arise from ruptured aneurysms?
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Posthemorrhagic vasospasm
Surgical vasospasm |
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What are the 2 most likely causes of a spontaneous intracranial hemorrhage in a patient <20 yo?
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-AV malformation
-Angioma |
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What is the most likely cause of a spontaneous intracranial hemorrhage in a middle aged patient between 20-60 yo?
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Ruptured aneurysm
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What is the most likely cause of a spontaneous intracranial hemorrhage in a patient >60 yo?
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Hypertensive hemorrhage
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At what age can hemorrhages secondary to blood dyscrasias be seen?
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Any
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What causes Hypoxic Encephalopathy?
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Any process that reduces the effective oxygenation of the brain
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What are some common causes of Hypoxic encephalopathy?
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-Reduced CO dt cardiac arrest
-Systemic hypotension -Respiratory failure dt asphyxia -Pulmonary/muscular diseases -Anemia/CO poisoning |
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What cells undergo necrosis in Anoxic encephalopathy? In what distribution?
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-Only neurons - not other cells
-Diffuse/scattered necrosis |
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How is necrosis caused by infarction different from anoxia?
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It will cause neuronal AND other cellular necrosis, and is more focal in distribution.
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What does the brain require all that oxygen for?
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Glucose metabolism
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So what condition can produce changes similar to those of anoxic encephalopathy?
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Hypoglycemia
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What type of cells are most often involved in Anoxic ischemia?
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Purkinje
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What is it called when neurons in one cortical layer are affected more than other layers?
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Laminar necrosis
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What is it called when necrosis is not limited to a layer?
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Pseudolaminar necrosis
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What is seen on gross exam of an anoxic encephalopathic brain
-early -later |
Early: swelling and edema
Later: neuron loss and gliosis |
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What determines the clinical course of Anoxic encephalopathy?
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severity and duration of anoxia
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What neurological manifestations will be seen in milder cases of Anoxic encephalopathy after recovery?
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-Dementia
-Spasticity |
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What neurological manifestations will be seen in severe cases of Anoxic encephalopathy?
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-Death due to anoxia
or -Death due to brain edema |
